The location of a portable electronic device may be determined using a global positioning system (GPS). As is known, a GPS-capable device determines its terrestrial location by triangulating its position relative to GPS satellites in orbit around the earth. This process includes receiving signals transmitted from the satellites, measuring the travel times of the signals from the satellites to the receiver, and then calculating the distances of the satellites from the receiver based on the travel time to derive a location value. The location value may be coordinates expressed using a standard reference system, such as the world geodetic system (WGS).
In another approach, assisted-GPS (or A-GPS) may be used to determine the location of the electronic device. A-GPS uses an assistance server to process location related data and access a reference network to speed location determination and to transfer processing tasks from the electronic device to the server. For instance, the assistance server may perform tasks to make range measurements and calculate position solutions that would otherwise be carried out by the electronic device.
Another location determining approach that is used in cellular telephone networks is to determine the identities of communications access points (e.g., “cell towers”) that are within communication range of the electronic device. Each cell tower may have an identifier (e.g., “cell ID”) and the identifier is communicated to the electronic device or a server. Each identifier, or cell ID, in a particular servicing network may be assumed to be unique and, therefore, may be used to indicate relative proximity to a certain location. In one embodiment, the cell ID and any related radio parameters may be used to generate a coordinate value through a radio network service. For example, under global system mobile communications (GSM) and universal mobile telecommunications system (UMTS) protocols, the position could be estimated through a mobile originated location request (MO-LR) to the network so that the electronic device position could be estimated using the network's knowledge of tower locations and antenna directions.
While GPS receivers are generally very accurate in determining position, they can become unreliable in indoor environments and, therefore, are not desirable for identifying a location of an electronic device within an indoor location, such as a home, office building, factory, etc. In addition, basing location on cell tower information is generally not accurate enough to distinguish relatively small differences in location that may occur when moving within a building.
The Bluetooth Special Interest Group (SIG) has proposed a technique for determining in-building location. In this proposal, a network of Bluetooth stations is deployed and the electronic device ranges on the stations as if the network were a miniature GPS system. However, this involves coordination among the stations, achieves an unnecessarily high degree of accuracy, and requires the electronic device to carry out steps that are not present in standard Bluetooth application specific integrated circuits (ASICs).